The Aikikai is the parent organization of Aikido and represents the last developments in the art of Aikido as taught by the Ueshiba family. The others are not only reflections of what the Founder taught at different times but they are also representations of what those individual leaders discovered and developed themselves.

IMHO this is not correct. Take a look at Nisho sensei. His aikido is a product of his being taught by osensei but also by his iaido, karate etcetera. His aikido is a very special line of aikido - within the Aikikai. I am sure there are many lines of aikido outside of the Aikikai, that technically are more mainstream than Nishio sensei.